wget: correctly handle rare case when we get EAGAIN _on first_ read

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 26 insertions, 6 deletions

diff --git a/networking/wget.c b/networking/wget.c
index f2d7daf2f..48688640a 100644
--- a/networking/wget.c
+++ b/networking/wget.c
@@ -487,6 +487,7 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
                                         rdsz = (unsigned)G.content_len;
                                 }
                         }
+
 #if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
 # if ENABLE_FEATURE_WGET_TIMEOUT
                         second_cnt = G.timeout_seconds;
@@ -497,22 +498,41 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
 # if ENABLE_FEATURE_WGET_TIMEOUT
                                 if (second_cnt != 0 && --second_cnt == 0) {
                                         progress_meter(PROGRESS_END);
-                                        bb_perror_msg_and_die("download timed out");
+                                        bb_error_msg_and_die("download timed out");
                                 }
 # endif
                                 /* Needed for "stalled" indicator */
                                 progress_meter(PROGRESS_BUMP);
                         }
 #endif
+                        /* fread internally uses read loop, which in our case
+                         * is usually exited when we get EAGAIN.
+                         * In this case, libc sets error marker on the stream.
+                         * Need to clear it before next fread to avoid possible
+                         * rare false positive ferror below. Rare because usually
+                         * fread gets more than zero bytes, and we don't fall
+                         * into if (n <= 0) ...
+                         */
+                        clearerr(dfp);
+                        errno = 0;
                         n = fread(G.wget_buf, 1, rdsz, dfp);
+                        /* man fread:
+                         * If error occurs, or EOF is reached, the return value
+                         * is a short item count (or zero).
+                         * fread does not distinguish between EOF and error.
+                         */
                         if (n <= 0) {
-                                if (ferror(dfp)) {
-                                        /* perror will not work: ferror doesn't set errno */
-                                        bb_error_msg_and_die(bb_msg_read_error);
-                                }
-                                break;
+#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
+                                if (errno == EAGAIN) /* poll lied, there is no data? */
+                                        continue; /* yes */
+#endif
+                                if (ferror(dfp))
+                                        bb_perror_msg_and_die(bb_msg_read_error);
+                                break; /* EOF, not error */
                         }
+
                         xwrite(output_fd, G.wget_buf, n);
+
 #if ENABLE_FEATURE_WGET_STATUSBAR
                         G.transferred += n;
                         progress_meter(PROGRESS_BUMP);